Observations on the distribution of the proteinpolysaccharide complex and collagen in bovine articular cartilage

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Abstract
The contents of collagen and chondroitin sulphate in bovine articular and nasal cartilage were determined by chemical analysis, and the distributions of collagen and proteinpolysaccharide in articular cartilage were studied by electron microscopy. Collagen was visualized, after osmium fixation, in Araldite sections stained with uranyl acetate or phosphotungstic acid (PTA), while the proteinpolysaccharide distribution was observed in Araldite sections of tissue which had been bulk stained with bismuth nitrate at low pH. The intercellular tissue is divisible into a pericellular zone and a main matrix. The pericellular zone exhibits fine fibres which are less than 250 Å in diameter: although they do not stain typically with PTA, they are probably collagenous in nature. The main matrix contains native collagen fibres which vary in diameter from 250-900 Å. Proteinpolysaccharide exists in the intercellular tissue in two states, namely, as free and randomly oriented macromolecules, and as macromolecules which are attached transversely over the a and b1 bands of each 640-Å period of the collagen fibres. The concentration of free proteinpolysaccharide is high throughout the pericellular zone, but diminishes practically to zero from the margin of the pericellular zone to the central part of the main matrix. No attached proteinpolysaccharide is present in the pericellular zone whereas a large amount is evident throughout the whole of the main matrix. It is suggested that this distribution conforms to the concept that the pericellular zone is a pool from which the proteinpolysaccharide, which has been synthesized by the neighbouring chondrocyte, migrates into the main matrix to effect the metabolic turnover of this tissue component.